Oriented strand lay-up

ABSTRACT

A process for continuously forming a product having elongated members at least about one foot long which are oriented, compressed and bonded is provided, the process comprising depositing elongated members on a moving carrier with an orientation that is substantially parallel to the direction of movement of said carrier, said members being deposited on said carrier over a length of carrier that is at least as long as about one and one-half times the length of the elongated members and is at least as long as about 30 times the final thickness of the compressed, composite product.

The present invention relates to a continuous process and apparatus fordepositing elongated members in a lay-up with each member orientedsubstantially in the longitudinal direction of the lay-up. The elongatedmembers may subsequently be bonded together into a composite product.

A product containing oriented elongated members or strands is disclosedin Barnes U.S. Pat. No. 4,061,819. That patent is directed to acomposite wood product which utilizes elongated wood strands. In suchproduct wood strands having a length in excess of about 2 feet arecoated with a resin and are positioned in substantially parallelrelationship in a long form which may have a width of, for example, 12inches. The strands are deposited with their ends in overlappingrelationship to provide a roughly uniform distribution along the lengthof the form. The strands are then compressed and heated to cure theresin and provide the final structural product which can have a strengthequal to prime structural lumber.

In preparation of composite strand products by batch methods, strandscan be positioned by hand with no significant loss in strength due todisoriented strands. However, when composite strand products are madeusing a continuous process, the strands are usually deposited on amoving conveyor belt so that the ends overlap. For example, the leadingedge of each strand will tend to overlap with strands preceding it ontothe conveyor while the trailing edge of the strand will tend to settlelower into the form. (See, e.g., Champigny U.S. Pat. No. 3,493,021). Theangles at which the strands are generally positioned are not random, butrather tend to be similar in both magnitude and direction. Hence, themajority of the strands may be oriented away from the horizontaldirection in mutually parallel fashion. Such a lay-up mat has what maybe referred to as "card-decking" orientation, in that each strand is atan angle to the longitudinal direction of the lay-up mat. It has beendiscovered that excessive vertical strand angle may also result invertical curvature in the continuously compressed product.

In the manufacture of composite products of the type disclosed in BarnesU.S. Pat. No. 4,061,819 regulation of the orientation of the elongatedmembers is important to obtain full product strength. If the strands arepositioned at an excessively large angle (either vertically orlaterally) to the longitudinal direction of the form, the compositeproducts tend to have less strength than their full strength potential.

As disclosed in the Barnes patent, wood strands which have been cut orsplit along the grain of the wood are normally used in making compositeproducts. However, when such strands are incorporated in a lay-up mat atsignificant angles to the horizontal, the product strength is reduced.Therefore, although formation of a composite product on a continuousbasis is desirable, the strength of the composite product may besignificantly lowered from the full strength potential.

It is an object of this invention to provide a continuous method formanufacturing a composite product in which elongated members areoriented substantially parallel to the longitudinal direction of thecomposite product.

It is a further object of this invention to provide a continuous methodof manufacturing a composite product substantially free of verticalcurvature in which elongated members are oriented substantially parallelto the longitudinal direction of the composite product.

It is another object of this invention to provide a continuous methodfor manufacturing composite structural lumber made up of elongated woodstrands.

It is still another object of this invention to provide apparatus forproducing composite products in which elongated members are orientedsubstantially parallel to the longitudinal direction of the compositeproducts.

It is also an object of this invention to provide a continuous methodand apparatus for manufacturing a composite product containing elongatedmembers in which the members have an average vertical angle of not morethan about 2°.

According to this invention, a process for continuously forming aproduct having elongated members at least about one foot long which areoriented, compressed and bonded is provided, the process comprisingdepositing elongated members on a moving carrier with an orientationthat is substantially parallel to the direction of movement of saidcarrier, said members being deposited on said carrier over a length ofcarrier that is at least as long as about one and one-half times thelength of the elongated members and is at least as long as about 30times the final thickness of the compressed, composite product.

It has been found that the problem caused by card-decking in theproduction of lay-up mats comprising elongated members such as woodstrands by continuous lay-up operations may be virtually eliminated bycontinuously laying strands at a substantially uniform rate over apredetermined length Y of a moving conveyor. More specifically,continuous lay-up procedures may be carried out so that verticalorientation of the elongated members is with X degrees of thelongitudinal direction in the continuous composite product. Generally, Xshould be not more than about 2°, preferably X is not more than about11/2°, more preferably not more than about 1°, and most preferably X isnot more than about 1/2°.

The parameters for such lay-up procedures are mathematically determined.The length (Y) of moving conveyor over which the strands should becontinuously laid is equal to the height (thickness) (Z) of thecompressed product being produced multiplied by the cotangent of Xdegrees. When X equals 2°, the cotangent is approximately 30 (28.6).Hence, (conveyor length)=30×(finished product height). Where X is 11/2°,the cotangent is approximately 40 (38.2), where X=1°, the cotangent isapproximately 60 (57.3) and where X is 1/2°, the cotangent isapproximately 110 (114.6). While the preferred maximum strand angle is2°, the general formula [Y=(cotangent X°)×Z] may readily be applied toachieve strand lay-ups with any other maximum degree of stranddisorientation, having a desired height (thickness) of the product inthe final compressed state. While depositing strands from a singlelocation onto a moving belt may be satisfactory if the coverage strandlength is long compared to the thickness of the mat, use of a singlelocation is not satisfactory if the length Y required for an angle X of2° is more than about one and one-half times the average length of thestrands employed and it is in such situations that the present inventionis useful.

The invention also provides apparatus for continuously laying elongatedmembers in a lay-up mat with each member oriented substantially in thelongitudinal direction of the lay-up at a low vertical angle. Additionalembodiments of the invention will be made clear in the discussion below.

The invention will be better understood by reference to the drawingswhich illustrate embodiments of the invention.

FIG. 1 is a schematic side elevational view of a conventional lay-upprocess according to the prior art.

FIG. 2 is a schematic side elevational view of a lay-up made accordingto the present invention.

FIG. 3 is a schematic cross-sectional side view of one embodiment of theapparatus of the present invention for laying elongated members in alay-up mat.

FIG. 4 is a front view of portions of the embodiment shown in FIG. 3.

FIG. 5 is an isometric view schematically showing an apparatus accordingto the present invention for producing composite products, including arotating drum assembly.

FIG. 6 is an isometric view schematically showing the rotating drumassembly also shown in FIG. 5.

FIG. 7 is an elevation of an alternative to the drum of FIG. 3.

FIG. 8 is a schematic isometric view showing another embodiment of theapparatus of the present invention for laying elongated members in alay-up mat.

FIG. 1 is a schematic illustration of the card-decking phenomenon asencountered in prior art lay-up procedures of the type disclosed, forexample, in Champigny U.S. Pat. No. 3,493,021. If elongated strands 10are placed on a conveyor 11 from a single source which does not movelongitudinally along the conveyor to form a lay-up mat 12, substantialcard-decking occurs. One end of each newly deposited elongated strandmay rest on the conveyor 11 but the strand will slope upwardly to reston a previous strand in the mat. FIG. 1 illustrates a situation in whichthe strands are oriented at a considerable angle.

FIG. 2 illustrates a lay-up mat made according to the present inventionin which elongated strands 10 are in a lay-up mat 21 such that theaverage angle of the strands is no more than about 2° to the horizontalin the compressed or final product. The dimension Y represents thelength over which elongated strands 10 are deposited at a substantiallyuniform rate in the lay-up mat 12. This dimension varies depending onthe desired height of the final product. The thickness of the finalproduct in relation to the height Z of the lay-up will vary somewhatdepending upon the strand dimensions and final product density. Asdiscussed below, when using wood strands, the ratio often will be aboutone-third with wood strands.

The elongated members or strands which are preferably employed in thepractice of this invention generally will have a length of at leastabout 1 or 2 feet and preferably a length of at least about 3 feet. Inany of the above cases, strands may have lengths of about 8 feet ormore. The strands will often have a width and thickness of from about1/16 inch to about 1 inch and more preferably from about 1/8 inch toabout 1/2 inch. It is possible and often probable that elongatedmembers, such as strands, used for assembly of a product will vary inlength from a minimum to a maximum length (e.g., from about 2 to about 8feet). In such case, the minimum length over which lay-up occurs isabout one and one-half times the length of the longest strands. As notedearlier, the strands are desirably wood strands that are split or cutparallel to the grain of the wood.

The strands may be coated with any suitable adhesive.Phenol-formaldehyde resins are commonly employed in the art for woodproducts and are preferred for the practice of this invention. Otherphenolics (e.g., containing resorcinol, cresol, or the like) as well asother adhesives, such as isocyanates, urea formaldehydes or others canalso be used in conjunction with the strands. While the invention willbe described with respect to strands coated with adhesive, it will beunderstood that the lay-up mat be formed and thereafter contacted withadhesive.

After the resin-coated strands are deposited as a lay-up mat containingoriented strands in a substantially uniform distribution, the mat iscompressed and the resin is cured (most often by heat) to produce thefinal product. The amount of compression will obviously vary dependingon a number of factors including the compressibility of the strands andthe desired density of the final product. A compression ratio of 3:1(i.e., a 12 inch high mat compressed to a 4 inch high final product) isnot uncommon and either higher or lower compression ratios can beemployed depending on the type of strands used and the desired densityof the final product. The selection of suitable compression ratios iswithin the skill of the art. Stated somewhat differently, the art canreadily select the thickness of mat which will provide the desiredproduct by simple preliminary compression tests. When wood strands areemployed, final products often will have a wood density (i.e., thedensity of the wood portion of the final product) of from about 1 toabout 11/2 times the original density of the wood. It should be notedthat the length of the lay-up in accordance with this invention isdetermined based on the final compressed thickness of the product. Mostoften, the final compressed product will have a thickness of at leastabout 1 inch and often at least about 2 inches. Indeed, having acompressed thickness of at least about 4 inches or at least about 8inches are feasible. The width of the lay-up can vary widely. Widths of12 inches to 30 inches or more are entirely feasible.

Generally, the lay-up mat will be conducted horizontally through a pressand be pressed vertically which will, of course, reduce the height ofthe lay-up. It is possible, however, that the mat can be pressed fromthe sides. In such event, the mat height will be substantially the sameas the finished height and angle calculations should be madeaccordingly.

An apparatus which may be used in the practice of the present inventionis illustrated in FIGS. 3 and 4. Elongated strands 10 are placedside-by-side in a substantially parallel relationship on a conveyor 30.The conveyor 30, which is positioned approximately midway of thetransverse travel of drum 33, moves the strands 10 in a direction, asshown by arrow A. The conveyor is desirably at least as wide as thestrands are long. Each strand 10 travels to the end of the conveyor 30and drops onto a guide 31 which directs it to the surface of rotatingdrum 33 at location 32. In the embodiment shown, the strands areretained in position 32 on the rotating drum by a friction surface(e.g., a paper machine felt fabric). Friction prevents the strand fromsliding on the drum surface. Other strand restraining means can also beemployed. For example, a drum with grooves can also be used.

Drum 33 rotates in the direction of Arrow B and also reciprocates alongthe drum axis 35 (FIG. 4, Arrow C) so that strands 10 are dropped ontodrum 33 in a progressive pattern as illustrated in FIG. 4. Theprogression of strand positioning preferably extends along the fulllength of the drum 33, but this is optional.

When the strands have traveled on the rotating drum 33 to apredetermined radial position 34, which is normally about a quarter of arotation, the strands 10 fall away from the drum 33 and into trough 37.The strands may be guided by sliding down a surface 36 whichreciprocates backwards and forwards across the width of a lay-up trough37 (as indicated by Arrow D in FIG. 3) so that the strands 10 aredistributed across the full width of lay-up 21. If desired, distributionacross the lay-up can be achieved by reciprocating trough 37 laterally.The lay-up trough 37 has a moving conveyor belt 39 and sides 38.

If desired, a flexible cover 40 may be positioned over the face of thechute 36 as shown in FIG. 3. The cover 40 serves to minimizeside-to-side flutter of strands sliding down the face of member 36, thusminimizing horizontal disorientation of strands. Such a cover may bemade out of flexible plastic, cloth, or the like.

The rotational and reciprocating speeds of the drum 33 are chosen sothat the residence time of a strand on the drum is approximately equalto a n+1/2 cycle time of the drum's reciprocating cycle (where n is aninteger). In other words, the strand residence time on the drum is, forexample, a 1/2, 11/2 or 21/2 multiple of the drum's reciprocating cycletime. The feed rate of strands to the drum will equal the deposit rateof strands into trough 37. The correlation of deposit rate of strandsinto the trough with conveyor speed is within the skill of the art. Itwill be appreciated from the above discussion that the drum will have aneffective length over which strands are carried (E) equal to one-halfthe lay-up length plus one-half the width of strands on the firstconveyor 30.

FIGS. 5 and 6 schematically illustrate an apparatus for the continuousmanufacture of a composite adhesively bonded product made fromsubstantially straight strands, such as wood strands. Strands 10 with anadhesive coating are placed side-by-side in a generally parallelrelationship and advance on a first conveyor means, e.g., conveyor 30.The strands 10 are conveyed on a conveyor 30 in the direction shown byarrow A. The strands 10 drop off the transverse conveyor 30 and aredirected by means of a guide 31 to the friction surface on a secondconveying means, e.g., a rotating drum 33.

As illustrated in FIGS. 3 and 4, the drum 33 rotates slowly and alsoreciprocates within a path in line with the drum axis so that thestrands 10 are deposited along the drum 33 in a progressive pattern. Asthe drum 33 rotates, the strands 10 fall onto a chute 36 whichreciprocates backwards and forwards, parallel to the strand length, tolay the strands 10 in a mat 21 (not shown) within a lay-up trough 37contained by stationary sides 38 and a third conveyor means, e.g.,conveyor belt 39. While the bottom of the trough is shown as angled, itcan be horizontal, if desired. The mat 21 on the conveyor 39 may beconveyed through a continuous press where the strands 10 in the mat 21are compressed and cured. For thermosetting resins such asphenol-formaldehyde heating may be employed to cure the resin.

As illustrated in FIG. 6, the drum 33 may be rotated by a gear drumdrive motor 60 and a chain drive 61. The drum drive motor 60 and drum 33are mounted on a trolley 62 which reciprocates in a predetermined pathby means of a chain 63 driven by a geared reciprocating motor system 64.As previously mentioned, the various factors can be correlated toprovide the desired height of the mat.

In one typical apparatus, the strand conveyor 30 had a width of about 9feet, and the drum 33 had a diameter of about 3 feet and a length of 21feet (with a strand receiving length of about 19 feet). The drumtransversely traveled 11 feet with a speed of about 30 seconds per cycleand a rotational speed of one rotation each 50 seconds. The lay-updistance was about 30 feet. The surface 36 moved back and forth in abouta 10-15 second cycle. The conveyor 36 was 12 inches wide and moved at aspeed of about 3/4 to 11/4 feet per minute.

An alternative to the drum 33 is shown in FIG. 7. In FIG. 7, the surface31 guides strands 10 to reciprocating conveyor 70 which is composed ofendless conveyor belt 71 which moves around guides 72 and 73 in thedirection shown by arrow G. Strands 10 are moved along the upper run ofconveyor 70 around guide 73 and move down surface 36 into trough 37having side walls 38 and conveyor 39. In the embodiment shown, conveyor37 is reciprocated back and forth as shown by arrows H to provide adistribution of strands 10 across conveyor 39. In one case, a conveyor70 such as shown in FIG. 7 had a width of about 311/2 feet and atransverse travel so that the lay-up distance was about 50 feet in orderto provide a lay-up mat thickness of about 12 inches and a consequentfinal compressed product thickness of about 4 inches.

The apparatus of FIG. 7 is equivalent to a drum of a very large radiussince the residence time of the strands on the upper run of conveyor 70is equivalent to the residence time of the strands on the drum surfaceand correlates with the reciprocating cycle. Moreover, since guides 73can have a relatively small diameter (e.g., 1 foot or less) the point atwhich the strands disengage from conveyor 70 remains relatively constantand can be closely controlled. Both the apparatus of FIG. 3 and of FIG.7 can be considered to include a rotating member, e.g., the drum 33 ofFIG. 3 and the conveyor 70 of FIG. 7.

Yet another embodiment of an apparatus for carrying out the process ofthe present invention is disclosed in FIG. 8. Strands 10 containingresin advance laterally on a transverse conveyor 80 in a directionsubstantially normal to their length and are deposited individually ontoa longitudinal conveyor 81 moving in a direction generally parallel (butin an opposite direction) to conveyor 39. The strands 10 move generallyin the direction of their length in a row 82 on the longitudinalconveyor 81 until the first strand 10 in the row 82 reaches apredetermined position on the longitudinal conveyor 81, when a lateralsweeping arm 83 (e.g., a brush, rubber strip, board, plate or the like)pushes the row 82 of strands 10 off the longitudinal conveyor 81 ontothe conveyor 39 in a trough 37 (not shown). The predetermined positionmay be, for example, near the end of the longitudinal conveyor 81. Theresulting mat is similar to that shown in FIG. 2. It will be appreciatedthat conveyor 81 may move forward and backward across conveyor 39 todeposit strands across the width of conveyor 39.

In a further embodiment, the longitudinal conveyor 81 is adapted to tipsideways when strands 10 reach the predetermined position on theconveyor 81, and the longitudinal conveyor 81 is positioned so that whenit tips sideways, the strands fall onto the mat conveyor 39. In thismanner, the sweeping arm 83 may not be needed. In still anotherembodiment, the longitudinal conveyor 81 may travel in substantially thesame direction as the lay-up conveyor 39, but at a higher speed so thatstrands 10 can be pushed from the longitudinal conveyor 81 to the matconveyor 39 to provide a substantially uniform rate of deposition. Itwill be understood that conveyor 39 can reciprocate laterally, or that areciprocating surface corresponding to surface 36 of FIG. 3 can beemployed, for example, to distribute strands laterally across conveyor39.

The lay-up systems of this invention can effectively align strandsparallel to the run of a continuous conveyor, in both vertical andlateral directions. However, it needs to be recognized that in anycontinuous mat with a depth beyond the thickness of one strand therewill be some card-decking. The systems also tend to maximize the minimumdistance between any two strand ends, which effectively reducesclustering of strand ends with a resulting area of weakness.

It is to be understood that while the apparatus embodiments disclosedeffectively may be used to carry out the process of the invention, anyother means capable of depositing layers of strands over a predeterminedlength of the lay-up conveyor to substantially eliminate card-deckingorientation, also may be employed. For example, strands may be depositedon a continuously moving conveyor in a trough from at least two lateralconveyors positioned on the same side of the conveyor or staggered oneach side of the moving conveyor on which the mat is being formed. Insuch embodiment, at least two transverse conveyors are positioned overthe lay-up trough and deposit strands onto the moving belt conveyor overthe desired length relative to the length of the strands and the finalthickness of the product as discussed earlier. The conveyors can beimmediately adjacent to each other or can be spaced from each other solong as the requirements for overall length of deposit are met. Theconveyor which holds the continuous lay-up mat can be reciprocated backand forth to provide strand deposit across the width of the lay-up, theend of the transverse conveyors can be reciprocated back and forth, or areciprocating guide means positioned below the transverse conveyors canbe used.

This invention is applicable to strands generally. Particular benefitsin reducing bowing is obtained when the product contains resilientstrands. Wood is a particularly preferred strand material. Othermaterials include, without limitation, fiber glass in a resin matrix andsynthetic or natural cords in an elastic matrix such as rubber.

It will be apparent to those skilled in the art that various changes maybe made in the details of the process and apparatus of the presentinvention as described herein and shown in the drawings withoutdeparting from the scope of the present invention which is limited onlyby the claims.

We claim:
 1. A process for continuously forming a composite producthaving elongated resin coated members at least about one foot long whichare oriented, compressed and bonded to provide a composite product whichcomprises depositing said elongated members on a moving carrier in alay-up trough with an orientation that is substantially parallel to thedirection of movement of said carrier, said members being deposited onsaid carrier over a length of carrier that is at least as long as aboutone and one-half times the length of said elongated members and is atleast as long as about 30 times the final thickness of the compositeproduct, thereafter compressing and bonding said elongated membersproducing said composite product where the average vertical orientationof said elongated members in said composite product is not more thanabout 2 degrees in a longitudinal direction.
 2. The process of claim 1in which said length of said carrier is at least as long as about 60times the final thickness of said composite product.
 3. The process ofclaim 1 in which said length of said carrier is at least as long asabout 110 times the final thickness of said composite product.
 4. Theprocess of claim 1 in which said elongated members are wood strands atleast about 3 feet long.
 5. The process of claim 2 in which saidelongated members are wood strands at least about 3 feet long.
 6. Theprocess of claim 3 in which said elongated members are wood strands atleast about 3 feet long.
 7. The process of claim 1 in which saidelongated members are wood strands at least about 8 feet long.
 8. Theprocess of claim 2 in which said elongated members are wood strands atleast about 8 feet long.
 9. The process of claim 3 in which saidelongated members are wood strands at least about 8 feet long.
 10. Theprocess of claim 1 in which the final thickness of said compressedcomposite product is at least about 4 inches.
 11. The process of claim 4in which said wood strands have a width and thickness of from about 1/16inch to about 1 inch.
 12. The process of claim 1 in which said elongatedmembers are at least about 3 feet long and have a width and thickness offrom about 1/16 inch to about 1 inch and in which the final thickness ofsaid compressed composite product is at least about 4 inches.